The formation of the oxide ion `O^2-(g)` from oxygen atom requires first an exothermic and then an endothermic step as shown below: `O(g)+e^ rarr O^-(g),delta _t H=-1.41kJ mol^-1`,`O^-(g)+e^- rarr O^2-(g),delta_t H=+1780 kjmol^-1` thus process of formation of `O^2-` in gas phase is unfavourable even though `O^2-` is isoelectronic with neon it is due to the fact that

Options

A. electron repulsion outweighs the stability gained by achieving noble gas configuration
B. `O^-` ion has comparatively smaller size than oxygen atom
C. oxygen is more electronegative
D. Addition of electron in oxygen results in larger size of the ion